Jamieson, Fausset and Brown on Matthew 21:44

44. And whosoever shall fall on this stone shall be broken: but on whomsoever it shall fall, it will grind him to powder--The Kingdom of God is here a Temple, in the erection of which a certain stone, rejected as unsuitable by the spiritual builders, is, by the great Lord of the House, made the keystone of the whole. On that Stone the builders were now "falling" and being "broken" (Is 8:15). They were sustaining great spiritual hurt; but soon that Stone should "fall upon them" and "grind them to powder" (Da 2:34, 35; Zec 12:2)--in their corporate capacity, in the tremendous destruction of Jerusalem, but personally, as unbelievers, in a more awful sense still.